DESCRIPTION: The long-term objective of this proposal is to gain insight into the molecular mechanisms involved in the clustering and postsynaptic targeting of type A receptors for y-aminobutyric acid (GABAA), the principal receptors that mediate neural inhibition in the mammalian CNS. The y2 subunit of GABAA receptors is essential for clustering and postsynaptic targeting of these receptors and gephyrin in vivo during development. However, it is not known whether the y2 subunit is required for maintenance of GABAA receptors and gephyrin at mature synapses. The first main objective is to determine whether the y2 subunit is required for maintenance of GABAA receptors and gephyrin at mature synapses, after synaptic localization of GABAA receptors has been established. To address this question, we will take advantage of mice that carry a conditional mutation in the y2 subunit gene that can be induced by Cre/loxP recombination. In particular, we will test whether the y2 subunit is still required for clustering after synaptic localization of GABAA receptors has been established. The second main objective is to identify and isolate novel factors that interact with GABAA receptor subunits and promote receptor clustering and targeting to specific postsynaptic sites. It is predicted that the differential subcellular distribution of GABAA receptor isoforms require specific factors to allow the discrimination of GABAA receptors with different subunit composition. Various fragments derived from several GABAA receptor subunits and gephyrin will be used as molecular probes to screen protein expression libraries.